Bypass air volume control device for combustor used in gas turbine

ABSTRACT

The invention applies to an air bypass control device which can bypass a portion of the compressed air in the space within the casing into the tail pipe connected to a combustion chamber via a control valve and a bypass channel. The invention includes a valve mechanism including a flat sliding ring, and a valve operating mechanism. The valve mechanism intersects a number of bypass air channels each of which is connected to a pipe located in the space inside the casing. A number of openings are arranged in the flat sliding ring for bypassing the air to the bypass air channels. The valve operating mechanism, one end of which is connected to the flat sliding ring, causes the flat sliding ring to rotate back and forth. When the operating mechanism rotates the flat sliding ring, the openings in the flat sliding ring rotate so as to coincide with or move away from the openings of the bypass channels. The control valve mechanism is made up of a flat sliding ring with a number of openings which corresponds to the number of bypass channels, and a ring supporting base which supports the flat sliding ring in such a way that the flat sliding ring can slide freely in the circumferential direction. One side of the openings of the flat sliding ring opens into the space in the casing, and the other side of the openings opens into the opening of the bypass channel when it is rotated.

TECHNICAL FIELD

This invention concerns a bypass air control device used to control thevolume of air bypassed from the combustion engine in a gas turbine. Morespecifically, it concerns a bypass air control device which bypasses avolume of compressed air in the casing of the combustion engine, inwhich a number of combustion chambers are arranged with tail pipes, bydiverting the compressed air into those tail pipes.

TECHNICAL BACKGROUND

The gas turbines used in electric power plants, nuclear power plants andvarious other industrial plants are velocity-type heat engines whichemploy as their operating medium their own operating gases, mainly airand combustion gases. These turbines basically comprise a compressor,which performs the adiabatic compression process; a combustor, whichheats the air-fuel mixture under constant pressure; and a turbine, whichperforms the adiabatic expansion process.

The combustor has a number of combustion chambers, each with a tailpipe, in the space in the casing which is pressurized by the air fromthe compressor. The combustion gases generated in the combustionchambers are conducted via the tail pipes to the turbine, which theycause to rotate.

In this sort of combustor, the air pressurized by the compressor isconducted to the space in the combustor casing at all times. Since theamount of the pressured air for combustion is proportional to the stateof combustion in the chambers (i.e., to the load fluctuation), and itfluctuates according to the state of combustion at all times, it isnecessary to bypass the pressurized air in the space in the casing inorder to maintain the air pressure at a constant level. In other words,a portion of the compressed air in the space is conducted via controlvalves or bypass channels into the tail pipes connected to thecombustion chambers, mixed with the hot, high-pressure combustion gasesin the pipes and released into the turbine, thus the pressure of the airin the space in the casing can be maintained at a constant level.

To be more specific, if the volume of air admitted to the bypasschannels is controlled by a valve or a valve-adjusting mechanism, and alarge volume of pressurized air is to be admitted to the combustionchamber, then the bypass valve can be constricted or closed by thevalve-adjusting mechanism so that the volume of air flowing into thebypass channels is reduced or entirely cut off. If a small volume ofpressurized air is to be admitted to the combustion chamber, the bypassvalve can be opened more or opened all the way so that the volume of airflowing into the bypass channels is increased. In this way the air inthe space in the casing can be maintained at a specified pressure.

The prior art design shown in FIG. 7 is a bypass air control device forcontrolling the volume of air which is bypassed. It consists of acontrol valve for the bypass channel and a mechanism for adjusting thevalve.

4 is the pressurized space inside casing 7 of the combustor. In thespace 4 under casing 7, a number of the combustion chambers (not shown)and the tail pipes 1 which are connected to them are arranged around thecircumference of the casing. (In the drawing, only casing 7 and theessential portion of a single tail pipe 1 are shown.)

A bypass channel consisting of elbow pipe 3 and bypass pipe 2 isconnected to the side of the tail pipe 1. Opening 2 a at the front ofthe bypass channel faces space 4 in casing 7. Pressurized air can bebypassed into the tail pipe 1 via the opening 2 a. A butterfly valve 5is inside the bypass pipe 2. This valve controls the volume of air whichis bypassed. Valve stem 19 of the butterfly valve 5 extends upward fromthe valve and is connected via a spline to adjustment shaft 17.

Shaft 17 is mounted to the outer surface of casing 7. Its operatingportion is inserted through casing 7; its front end is connected via aspline to valve stem 19 of the butterfly valve 5.

Annular inner ring 9 is fixed on the outer periphery of the exterior(i.e., the upper surface) of the casing 7. The upper surface of theinner ring 9 is shaped into a rectangular depression. Shaft rollers 9 aare mounted along the entire periphery of inner ring 9, so that outerring 11 can freely move in contact with them in the bottom of thedepression.

The bottom of outer ring 11 has a rectangular protuberance which engagesin the shaft rollers in the inner ring 9 in such a way that it is freeto rotate. The inner surface of the outer ring 11 and the upper end ofadjustment shaft 17 are connected by link 13 and lever 15, which convertthe rotational movement of the outer ring 11 to rotational movement ofadjustment shaft 17.

Thus when outer ring 11 rotates in the peripheral direction with innerring 9 as a guide, adjustment shaft 17 is caused to rotate via link 13and lever 15.

Because adjustment shaft 17 is connected to valve stem 19 of butterflyvalve 5 via a spline, the rotation of shaft 17 is linked to the rotationof valve stem 19, and valve body 21 of valve 5 can be made to open andclose.

Thus the rotation in of outer ring 11 the circumferential direction onthe outer surface of the casing 7 can be converted to a force whichdrives valve body 21 of butterfly valve 5 in bypass channel 2 and 3within casing 7 to open or close. In this way it is possible to adjustthe rate at which the air bypass control valve is opened, and with it,the volume of air which is bypassed.

In this sort of prior art air bypass device for controlling the volumeof air, valve body 21 of butterfly valve 5 is made of a lightweightmaterial, so vibration resulting from combustion could be transmittedvia the tail pipe from the combustion chamber to the bypass channel.When this happened, the resonant vibration of the pipe would cause thevalve body in the channel to stutter. This would result in greatlyaccelerated abrasion of the valve body, the shaft and the bearings forthe valve stem in the bypass channel.

DESCRIPTION OF THE INVENTION

The object of this invention is to provide a bypass air control devicefor controlling the volume of air bypassed used in the combustion engineof a gas turbine in which, even when the combustion vibration describedabove occurs, the structural components of the control valve and itsrelated hardware would not experience vibration, and in which theopening and closing of the bypass could be controlled in a reliable andstable fashion.

Another object of this invention is to provide a bypass air controldevice for controlling the volume of air bypassed in which the links orother connectors between the valve in the bypass channel for controllingthe volume of air and the mechanism for adjusting that valve, which isplaced on the exterior surface of the casing, can easily absorb anythermal expansion or assembly error which might occur.

Still other objects of this invention will be made clear from thedisclosure which follows.

To achieve these objects, the present invention has been designed asfollows. It pertains to a combustion engine for a gas turbine which has,in a space within the casing pressurized by compressed air fed into itfrom a compressor, a number of combustors comprised of combustionchambers and the tail pipes connected to them. The invention applies toan air bypass control device which can bypass a portion of thecompressed air in the space within the casing into the tail pipeconnected to a combustion chamber via a control valve and a bypasschannel.

The invention is distinguished in the following ways, it comprises avalve mechanism including a flat sliding ring, and a valve operatingmechanism. The valve mechanism intersects a number of bypass airchannels, each of which is connected to a pipe located in the spaceinside the casing. The bypass air channels are located at a circularposition in the casing. A number of openings are arranged in the flatsliding ring of the valve mechanism corresponding to the number ofbypass air channels for bypassing the air to the bypass air channels.The valve operating mechanism for the valve, one end of which isconnected to the flat sliding ring, causes the flat sliding ring torotate back and forth in the circumferential direction.

When the valve operating mechanism rotates the flat sliding ring througha certain angle, the openings in the flat sliding ring rotate so as tocoincide with or move away from the openings of the bypass channels. Inthis way it is possible to control the area of the openings of thebypass channels.

The control valve mechanism comprises a flat sliding ring with a numberof openings which corresponds to the number of bypass channels, and aring supporting base which supports the flat sliding ring in such a waythat the flat sliding ring can slide freely in the circumferentialdirection. One side of the openings of the flat sliding ring opens intothe space in the casing, and the other side of the openings opens intothe opening of the bypass channel when it is rotated. A portion of thecompressed air from the pressurized air space in the casing can beconducted through the ring openings into the openings of the bypasschannels.

With this invention, then, there is no longer a control valve for eachof a number of bypass channels, which number corresponds to the numberof tail pipes which are in the space in the casing of the combustionengine. Rather, there are only one or two control valves for all of thebypass channels. (As shall be explained in the embodiments which follow,the basic design calls for a single valve. However, two of the flatsliding rings described above may be laid one atop the other in aconcentric fashion, with one serving as the valve for the odd-numberedbypass channels and the other as the valve for the even-numberedchannels.) A number of bypass channels can thus be controlled by one ora few flat sliding rings which slide over the openings of the bypasschannels, and one or several valve operating mechanisms will suffice.This is a much simpler configuration than is used in the prior art, andit allows the parts count to be greatly reduced.

Furthermore, because the flat sliding rings do not control the bypasschannels individually, but globally, any vibration generated bycombustion which is transmitted via the tail pipes will tend to bemutually cancelled. Even if it is not, the self-induced vibration of therings will be substantially mitigated because they are much more massivethan butterfly valves.

The fact that self-induced vibration is substantially eliminated meansthat components which experience friction will abrade more slowly; andsince the frictional parts are not shafts, but a flat sliding ring whichcontacts the entire surface, only minimal abrasion will occur.

The flat sliding ring is not pivoted on an axis like the butterflyvalves in prior art devices. Rather, it is a large-diameter ring whichcovers all of a number of bypass channels (16 in the embodiments whichfollow) placed at the periphery of the space in a cylindrical casing.The operating mechanism for the flat sliding ring is connected to oneside (say, on the outside) of the ring, so the angular rotation of theflat sliding ring can be shorter than the travel of the operatingmechanism. This enables the flow to be controlled more accurately.

As the following embodiments will show, the valve operating mechanismdiscussed above may consist of links or gear mechanisms.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of the essential parts of a bypass air controldevice which is a preferred embodiment of this invention for controllingthe volume of air bypassed.

FIG. 2 is a perspective view of the components comprising the flatsliding ring in the device described above for controlling the volume ofair bypassed.

FIG. 3 is a partial cross section of FIGS. 1 and 2, which shows how theflat sliding ring and the bypass channels meet and how the ring is fixedto the casing.

FIG. 4 is a partial cross section of FIGS. 1 and 2, which shows how thesliding rollers on top of the flat sliding ring engage with the valvesupporting base.

FIG. 5 is a cross section of the side on which the valve operatingmechanism is mounted to the device for controlling the volume of airbypassed, which shows the major structural components of the valveoperating mechanism.

FIG. 6 is an exploded perspective view of the other side of the valveoperating mechanism of FIG. 5.

FIG. 7 is a cut-away perspective view of a prior art device forcontrolling the volume of air bypassed.

DESCRIPTION OF PREFERRED EMBODIMENTS

In the following section a detailed explanation of this invention willbe given with reference to the drawings. To the extent that thedimensions, materials, shape and relative position of the componentsdescribed in this embodiment are not definitely fixed, the scope of theinvention is not limited to those specified, which are meant to servemerely as illustrative examples.

FIG. 1 is a side view of the essential parts of a bypass air controldevice for controlling the volume of air bypassed which is a preferredembodiment of this invention. FIG. 2 is a perspective view of thecomponents comprising the flat sliding ring in the device forcontrolling the volume of air bypassed.

FIG. 3 is a partial cross section of FIGS. 1 and 2. It shows how theflat sliding ring and the bypass channels meet and how the ring isattached to the casing.

FIG. 4 is a partial cross section of FIGS. 1 and 2, which shows how thesliding rollers on top of the flat sliding ring engage with the valvesupporting base.

In these drawings, casing 7 of the combustion engine is cylindrical.Pressurized air from a compressor (not shown) is conducted to itsinterior, where it pressurizes space 4. Sixteen bypass channels 2/3 (seeFIG. 2), each of which comprises an elbow pipe 3 and a bypass pipe 2,are arranged around the circular periphery of the casing 7 at regularintervals so that their openings 2 a face space 4 of casing 7 at a pitchof 22.5°. As can be seen in FIG. 7, the elbow pipes 3 which constitutebypass channels 2/3 are connected to the side part of tail pipes 1. Thepressurized air from the openings 2 a of the bypass channels can bebypassed into the tail pipes 1.

Valve mechanism 30, the ring-shaped valve for controlling the volume ofair bypassed, runs along a hypothetical circle which connects theopenings 2 a of all the channels in such a way that it can seal all theopenings. The openings 2 a of the sixteen bypass channels are arrangedat regular intervals around the periphery of the casing 7. Valvemechanism 30 comprises a flat sliding ring 33, a large-diameterring-shaped sliding panel which corresponds to the hypothetical circleconnecting the openings 2 a of the sixteen bypass channels, and a ringsupporting base (holder of the ring) 31, which supports the flat slidingring 33 so that it can freely slide in the circumferential direction.

Flat sliding ring 33, which is shown in FIG. 2, consists of ring-shapedpanel 35, in which are opened, at an angular pitch of 22.5°, which isthe same pitch as openings 2 a of bypass channels 2/3, a number ofopenings 37 equal to the number of the openings 2 a; and eight guiderollers 39, which are placed on the upper surface of the ring-shapedpanel 35 at a pitch of 45° and supported in such a way that they arefree to rotate.

There may be either 1×16 bypass channels 2/3 corresponding to the numberof tailpipes, or 2×16 bypass channels 2/3; in the latter case, thenumber of the openings 37 likewise corresponds to the number of bypasschannels 2/3.

As should be clear from FIGS. 1 and 4, the guide rollers 39 are ofapproximately the same diameter as the groove between the inner wall 31a of ring supporting base 31 and its outer wall 31 b. The guide rollers39 are in frictional contact with either inner wall 31 a or outer wall31 b as they rotate. In this way the ring-shaped panel 35 can rotateconcentrically to cylindrical casing 7 with a high degree of accuracy.

Ring supporting base 31, which supports the sliding ring 33 so that itis free to rotate, has the form of a round valve supporting base. As ismade clear by FIG. 3, it is fixed to casing 7 by flange 32 a on itsouter periphery.

As can be seen in FIG. 3, ring supporting base 31 has a dualconstruction so that it can enclose ring-shaped panel 35. Flanges 31 dand 32 a on either segment of the ring supporting base are joined bybolt 34 to form a single entity.

As can be seen in FIG. 1, a portion of the outer wall of the ringsupporting base 31 is cut away, and the outer periphery of sliding ring33 is exposed in this cut-away portion 31 c.

Mounting seat 43 is mounted to the exposed outer edge of sliding ring33. As can be seen in FIG. 1, adjustment link 50 is connected to thering through the mounting seat 43 and clevis 51.

Adjustment link 50 extends to the outer surface of casing 7. At thissurface it is mounted through clevis 67 to crank lever 69, which issupported by bracket 71 in such a way that it is free to pivot. Thecrank lever 69 is connected to actuator 81 through connecting rod 77.

When actuator 81 travels back and forth, crank lever 69 is caused topivot by connecting rod 77. This pivoting motion is conveyed throughclevis 67, causing connecting rod 59 of adjustment link 50 to travelback and forth. This motion is conveyed through clevis 51 and mountingseat 43, causing sliding ring 33 to rotate back and forth through agiven angle.

The range of rotation of sliding ring 33 should be such that when thering is rotated through a given angle, the openings 37 in the ring movefrom a position in which they completely overlap openings 2 a of thebypass channels 2/3 to a position in which they are completely separatedfrom those openings. In this way the area 36 of the opening of each ofthe bypass channels 2/3 can be controlled accurately.

Adjustment link 50 is supported on casing 7 in an airtight fashion.

FIG. 5 shows the area around the adjustment link where the flat slidingring of the valve operating mechanism is mounted. This flat sliding ringis the main component of the device for controlling the volume of airbypassed. FIG. 6 shows the area around the connecting rod on the otherside of the valve operating mechanism in FIG. 5.

In FIG. 5, one end of clevis 51 is attached through connecting pin 55and bushing 53 to mounting seat 43 in such a way that the clevis is freeto pivot. The other end of clevis 51 is screwed onto one end ofconnecting rod 59. Connecting rod 59 is inserted into support sleeve 57,which is fixed to casing 7. Rod 59 projects beyond casing 7, and itsexposed end is screwed into Joint 61.

The portion of support sleeve 57 which comes in contact with mountingpanel 54 on the outer surface of casing 7 is machined into a sphericalsurface to form a tight seal and prevent any air leaks.

Joint 61, which is screwed to the end of connecting rod 59, is connectedthrough spherical bearing 63 and connecting pin 65 to one end of clevis67. The other end of clevis 67, as can be seen in FIG. 1, is connectedto one of the free ends of triangular crank lever 69.

As is shown in FIG. 1, the base of crank lever 69 is supported bybracket 71 in such a way that it is free to pivot. Bracket 71 is fixedto the outer surface of casing (i.e., combustion chamber housing) 7. Ascan be seen in FIG. 6, the other free end of crank lever 69 is connectedthrough clevis 73 and connecting rod 77 to actuator 81. It is connectedto the clevis by a pin which is inserted through holes 69 a and 73 a.Connecting rod 77 has such clevises (73 and 75) on either end.

When a pin 76 is inserted through holes 69 a and 73 a (or 75 b) inclevis 73 (or 75), bracket 71 or actuator mount 74 is supported in sucha way that it is free to pivot on clevis 73 (or 75).

The end 77 b of rod 77 which connects to clevis 73 has a left-handedthread; the end 77 a which connects to clevis 75 has a right-handedthread. These work together with hole 75 a of clevis 75 and the hole(not shown) in clevis 73 to form a turnbuckle.

Rotating connecting rod 77, then, will adjust the distance betweenclevises 73 and 75 to produce the appropriate connection between link 50and actuator 81.

Once the connection between rod 77 and clevises 73 and 75 has beenadjusted, lock nut 78 is tightened onto the left-handed screw and locknut 79 onto the right-handed screw.

The amount of play in the connection between clevis 73 and crank lever69 and that between clevis 75 and actuator 81 can be increased throughthe use of spherical bearings and pins like the bearing 63 and pin 65.

In this embodiment, a link 50 assembled like that shown in FIG. 1 isused to cause flat sliding ring 33 to travel back and forth in thecircumferential direction when actuator 81 moves back and forth. In thisway the amount of overlap 36 between openings 37 in the ring andopenings 2 a of bypass channels 2/3 can be controlled. By adjusting thearea of the overlapping openings, the volume of air that is bypassed canbe adjusted.

Ring-shaped panel 35 of flat sliding ring 33 engages frictionally ingroove 32 of ring supporting base 31. A specified degree of frictionalresistance operates during its rotation to mitigate vibration.

The changes occasioned by different rates of thermal expansion among thecomponents around link 50 will be absorbed by the universal jointscomprised of connecting pins and spherical bearings.

Effects of the Invention

With the invention described above, vibration due to combustion in acombustion chamber will not translate into vibration of structuralcomponents of a control valve. Combustion vibration will not result inself-induced vibration, and the abrasion of components which experiencefriction will be mitigated. The opening and closing of the bypass can becontrolled reliably and stably.

Furthermore, with this invention, any thermal expansion or assemblyerror experienced by connectors such as the links between the controlvalve in the bypass channel and the valve adjustment mechanisms on theouter surface of the casing can easily be absorbed.

Other effects may also be achieved.

What is claimed is:
 1. A bypass air control device used in a gas turbinecombustor in which a number of combustion chambers with tail pipes arearranged in a pressurized space of a combustor casing, which bypasses avolume of compressed air in said pressurized space fed from acompressor, by diverting the compressed air into the tail pipes viabypass valves and bypass air channels, comprising: a flat sliding ring,which intersects a plurality of the bypass air channels and has aplurality of openings corresponding to openings of said bypass airchannels, and a valve operating mechanism to control an opening/closingdegree of the openings of said bypass air channels by rotating said flatsliding ring back and forth in a circumferential direction.
 2. A bypassair control device used in a gas turbine combustor according to claim 1,wherein said valve operating mechanism comprises said flat sliding ringhaving a number of said openings which corresponds to the number of saidbypass air channels, and a ring supporting base which supports said flatsliding ring in such a way that said flat sliding ring can slide freelyin the circumferential direction, and one side of said openings of saidflat sliding ring opens to said pressurized space to conduct a portionof said compressed air into said openings of said bypass channels.
 3. Abypass air control device used in a gas turbine combustor according toclaim 1, wherein said valve operating mechanism includes a connectingrod connected at one end to said flat sliding ring through a pivotsupport and another end extending to an outer surface of the combustorcasing so as to rotate said flat sliding ring back and forth through acertain angle when an actuator moves the connecting rod back and forth,whereby the openings in said flat sliding ring rotate to coincide withor move away from said openings of said bypass air channels when saidvalve operating mechanism rotates said flat sliding ring through theangle in order to control an overlapped area of said openings of bothsaid flat sliding ring and said bypass air channels.